Which word fits better in this sentence?

niche "strength" and "talent" are also OK, If I have to pick from those, I'd choose "strength", because "talent" is more specific to arts - such as singing or acting, whereas "strength" is quite a generic term for ability within vocational subject areas.

P.S. re. "...also learn from other people of the same field to improve." Better, "also learn from *others within* the same field." "to improve" is rather tautological, because learning implies improvement.

Neither, really. "Find one's strength" *is* an expression, though it refers to literal strength; "find one's talent" is not really a phrase (not that you *couldn't* use it). So I guess the intended answer is *strength*. But really neither is something people would normally say in English.